A gas turbine engine includes a compressor typically comprising a plurality of axial stages which compress airflow in turn. A typical axial compressor includes a split outer casing having two 180 degree halves, which are suitably bolted together. The casing includes rows of axially spaced apart casing slots which extend circumferentially for mounting respective rows of vane segments.
A typical vane segment includes radially outer and inner shrouds between which are attached a plurality of circumferentially spaced apart stator vanes. The outer shroud includes a pair of axially spaced apart forward and aft hooks. The casing includes complementary forward and aft grooves which extend circumferentially within each of the casing slots for receiving the corresponding hooks in a tongue-and-groove mounting arrangement.
During assembly, the individual vane segments are circumferentially inserted into respective ones of the casing halves by engaging the forward and aft hooks with the corresponding forward and aft grooves. Each vane segment is slid circumferentially in turn into the casing slot until all of the vane segments in each casing half are assembled. The two casing halves are then assembled together so that the vane segments in each casing slot define a respective annular row of adjoining vane segments for each compression stage.
In this configuration, the individual vane segments are mounted to the outer casing solely by their outer shrouds, with the vanes and inner shrouds being suspended therefrom.
During operation of the compressor, each vane segment experiences stage differential pressure and airflow impingement, resulting in longitudinal, circumferential, and radial loads being transferred to and through the forward and aft hooks of the vane segment. Those steady loads are combined with pulsating blade-passing aerodynamic excitation loads, which cause the airfoil and outer shroud of the vane segment to vibrate. The vibrations in the outer shroud cause the forward and aft hooks to move within the forward and aft grooves. Such movement results in frictional wear between the outer shroud and the engine casing, which wear reduces part life.